S34 M. Beudant on the Opals Hungary. 
other times it is interposed in small layers in the substance of 
various kinds of opal. 
Stalactitic opal {Vopal concretionnee)^ transparent, translu- 
cid, or opaque, is still found in certain fissures of which it 
lines the walls, or in geodes : these are composed of small sta- 
lactites, which adhere more or less firmly to one another, and 
which, when limpid, differ in no respect from hyalite. They 
also assume a pearly lustre, when slightly heated, lose their co- 
herence, and break into small scales when exposed to a red 
heat. Their aggregation gives rise to masses which have the 
appearance of being homogeneous, and present the aspect of 
opals similar to some one of the varieties already mentioned, 
and even to the iridescent opal. Sometimes the stalactites are 
extremely minute, and completely fill up the irregular cavities ; 
the small fissures by which the siliceous matter has penetrated 
into the rock being equally filled. 
In some instances, the opaline matter has formed on the 
walls of the fissures only a very thin layer, which presents the 
appearance of minute tortuous canals, having their surface 
covered with very minute stalactitiform points lying lengthwise. 
These surfaces often present the aspect of certain earthy pu- 
mices, with elongated and tortuous vesicular cavities. 
Iridescent opal (Topale irisee), which is the principal object 
of research, is also plentifully disseminated in the rocks, but al- 
most always in extremely minute nests ; it is very rarely that it 
occurs in large pieces, like the other varieties. The working 
sometimes goes on for years before a piece occurs of the size of 
a twenty sous piece. The largest which has ever been found, 
in as far as I know, is that of the imperial cabinet of Vienna ; 
it is of the size of one’s fist, and weighs 17 ounces. This mag- 
nificent specimen has been known at Vienna for more than two 
centuries, and it is neither known at what period nor how it was 
obtained. It is polished irregularly to avoid diminishing its size. 
There are many fissures in it, and it is not completely disenga- 
ged from the matrix. 
The colours presented by this kind of opal are extremely 
various ; all the tints of blue, violet, redj yellow, green, &c. are 
blended in a thousand different ways, and present the most 
brilliant and agreeable reflections. This beautiful stone is also 
